<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script type="text/javascript">
        var s="123";
        var a=123;
        document.write(s==a+"  ");//只是两个数值相比较 ,空格不识别  使用nbsp；
        document.write(s===a+"  ");//数值和类型也会比较，s和a类型不同，所以为false
        var ab=12;
        var bc=13;
        document.write("ab>bc"+ab>bc);
        ab+=bc;
        document.write("ab+=bc"+ab);
        /*while循环*/
        var first_num=4;
        var second_num=3;

        var count=1;
        var num=1;
        while (Math.abs(first_num)-Math.abs(second_num)>Math.pow(10,-6)){
            first_num=4*(1/(Math.pow(-1,num-1)*(count)));
            second_num=4*(1/(Math.pow(-1,num)*(2*count+1)))
            count=2*count+1;
            num++;
        }
        document.write(first_num)
    </script>
</head>
<body>

</body>
</html>